This invention relates to a brake. It relates more particularly to a sprocket-actuated brake for use on a chain driven bicycle.
The brakes commonly found on present-day bicycles fall generally into two categories. There is the hand-actuated caliper brake usually installed on multiple speed bicycles and the pedal-actuated departure brake installed in the rear wheels of single speed bikes, such brake being actuated through the chain by applying a reverse torque to the pedal sprocket. Recent U.S. government regulations have been established requiring bike brakes to meet certain standards. Although the above brakes do meet those standards, they are quite expensive, indeed too expensive to be installed on present-day, low cost, single speed, chain driven sidewalk bikes used by small children.
Recently there has been developed a low cost bike brake whose shoe is urged into frictional engagement with the tire on the rear wheel when a reverse torque is applied to the pedal sprocket. The brake mechanism includes a U-shaped brake shoe which is pivotally supported by a bracket secured to the bicycle frame opposite the tire. An arm, one end of which is pivotally connected to the shoe, has its opposite end engaging the teeth on the pedal sprocket. When the pedal sprocket is rotated in the forward direction to propel the bicycle, the arm end simply rides on the sprocket teeth. However, when the rider applies a reverse torque to the pedal sprocket, the sprocket teeth engage the arm and push it rearwardly so that the arm presses the brake shoe against the bicycle tire thereby bringing the vehicle to a stop. A brake such as that is disclosed in U.S. Pat. No. 3,774,732.
That particular brake has several drawbacks which have militated against its full acceptance in the marketplace. It requires a special bike frame and pedal sprocket. Also, as the rider rotates the pedal sprocket to propel the bicycle, the arm of the brake mechanism rides on the sprocket teeth thereby producing a noisesome chattering or ratcheting noise which is annoying to the rider and to others in the vicinity of the moving bicycle.
We are also aware of a variation of that construction which includes a pair of metal plates which engages circular ribs on opposite faces of the pedal sprocket to bias the toothengaging portion of the arm away from the sprocket when the bike is pedalled in the forward direction to minimize that noise. However, that brake still requires a special pedal sprocket and indeed a special bike frame for its installation. It still has a relatively large number of parts. It is not particularly efficient in that much of the braking force applied by the rider is lost in its various linkages. Moreover its sprocket-engaging arm does not always bottom in the links between the sprocket teeth so that the applied battery force varies.
Furthermore, it has been found that the stop-length versus force characteristic of that prior brake is not linear. As the rider turns the pedal sprocket in reverse through a selected angle, the amount of force transmitted through a selected angle, the amount of force transmitted through the arm to the brake shoe varies so that the braking force applied by the shoe to the rear tire also varies. Resultantly, unless the rider compensates for the nonlinearity by easing up on the pedals, a bicycle may come to a very sudden stop and cause the rider to lose control of the bike. It is believed that the non-linear stop-length versus force characteristic of that prior brake is due to the fact that the angle which the arm makes with the sprocket and shoe changes to a considerable extent during operation of the brake thereby changing the amount of torque applied to the brake shoe as the sprocket is rotated in reverse to stop the bike.
The prior brake construction also has too many parts and requires a special stop lug to limit the pivotal motion of the shoe toward the tire. Otherwise, its sprocket-engaging arm might become bound up on the sprocket thereby rendering the brake inoperative.